Dry film developing apparatus

ABSTRACT

A platen for developing a web of exposed dry film by bringing sequentially discrete areas upon the film into contact with a heated platen. The platen surface is specifically constructed to offset wrinkling produced in the film at the thermal boundaries to the development zone.

O United States Patent [191 [11] 3,826,896 Thompson July 30, 1974 DRY FILM DEVELOPING APPARATUS 3,371.915 3/1968 Kawamura et a1. 95/94 R x 1 Inventor David p m Fairpom 312323319 21133? 21135,?if.?TY:.1111111111:111:11151/43 3 3 Assigneez Xerox Corporation, Stamford, 3,739,143 6/1973 Amundson et a1 219/216 Conn.

[22] Filed: July 9, 1973 Primary ExaminerFred L. Braun [21] Appl. N0.: 377,888

[52] US. Cl. 219/388, 100/93 P, 100/295, [57] ABSTRACT [51] Int Cl 156/499, 219/2l6l%2%7 b /9 )z A platen for developing a web of exposed dry film by b i gi g q ti lly di t areas p th i t [58] held of Search 95/89 94 R; 219/216 contact with a heated platen. The platen surface is 219/388; 34/152; 156/499; 100/93 295 specifically constructed to offset wrinkling produced in the film at the thermal boundaries to the develop- [56] References Clted mem Zone UNITED STATES PATENTS 3,177,793 4/1965 Stewart 95/89 R X 10 Claims, 3 Drawing Figures ATENTED M30574 3.826.898

' sum an? 2 o l 59 q) 5(I 50 (b) WWW FIG. 3

1 DRY FILM DEVELOPING APPARATUS This invention relates to a heated platen for continually developing in sequence discrete exposed regions upon the web of dry film.

In recent years many different types of film have been devised which, upon exposure to a light image, can be developed by simply heating the film to a temperature which is at or above the thermal developing threshold of the emulsion contained thereon. Typical of such dry films is a silver halide based film manufactured by the Minnesota Mining and Manufacturing Co. of St. Paul, Minn., which is described in greater detail in U.S. Pat. No. 3,455,075. Heretofore, dry film has generally been processed as cut strips of material with each strip containing a discrete exposure format or frame thereon. As described in greater detail in US. Pat. No. 3,608,466 the exposed film strip is placed within a heated development zone and the entire strip then heated to substantially the same temperature. As such, any deformation or shrinkage of the film induced by the heating process is uniform and unwanted wrinkling of the film is avoided.

On the other hand, it has been found that when a continuous web of film is sequentially developed within a heated region, a thermal gradient is created within that portion of the web situated adjacent to the developing zone. The temperature within this thermal boundary region attenuates outwardly from a maximum temperature at the interface to the developing zone to a minimum temperature wherein the web returns to ambient temperatures. Because of the relatively high developing temperatures involved and the nature of most dry films, internal stresses cause the heated film to shrink and exert a compressive stress on the undeveloped film at the development zone interface. Consequently, the film buckles causing wrinkles that decrease in amplitude as the distance from the interface increases. The magnitude of shrinkage exceeds the strain associated with thermal expansion. Normally, when processing a continuous web of film, this wrinkled area would be treated as unusable waste which, of course, considerably increases the processing costs. Furthermore, the automatic handling and processing of the unusable wrinkled web has proven tobe extremely difficult and time consuming.

It is therefore an object of the present invention to improve the processing of dry film and, in particular to the processing of dry film in a web configuration.

It is a further object of the present invention to eliminate waste when processing a web of dry film.

It is another object of the present invention to provide a dry film developing system which will substantially remove heat induced wrinkles from exposed dry film during processing.

These and other objects of the present invention are attained by a heated film developing platen having a working surface thereon for contacting, under tension, a discrete area of exposed film containing heat induced wrinkles along a portion thereof, the working surface of the platen having a first region thereon capable of contacting the previously wrinkled film area having a radius of curvature that increases inversely in relation to the intensity of wrinkling contained on said film whereby the normal forces acting upon the wrinkle containing film vary in proportion to the intensity of wrinkling, and a second region for contacting the nondeformed film area within the development zone having a uniform radius of curvature whereby the normal forces exerted upon the non-deformed portion of the film are relatively constant.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective view showing apparatus for automatically processing a web of dry film embodying the teachings of the present invention;

FIG. 2 is an enlarged end view showing the heated platen surface of the present invention for developing discrete areas upon the web in process;

FIG. 3 is a top view of a typical web illustrating heat induced wrinkles upon the film surface which are produced at the input thermal boundary to the developing system.

Most commercially available dry films tend to shrink to some degree when subjected to the high temperatures required for development primarily due to the nature of the support materials known and used in the art. When an entire strip of film is placed within a heated development zone, the shrinkage is more or less uniform and the film, after development, is generally free of wrinkles or other heat induced deformations which would adversely effect the density of the images thereon. However, in automatic film processors, it is highly desirous in terms of design considerations to process film in a web configuration, the web containing a series of exposures or frames thereon which are separated by a minimal amount of interconnecting unexposed film. The use of a web greatly simplifies registration and handling of the film as it moves through the various processing stations involved.

As noted above, it has been found that wrinkling problems arise when discrete segments upon a web of dry film are sequentially processed within a heated development zone. The term film wrinkling, as herein used, refers to a heat induced deformation within the web that manifests itself as a dimensional decrease across the width of the web that causes the film material to become buckled or wrinkled. Investigations involving this particular phenomena have established that during heat development a wrinkled zone is created within the web material which diminishes along the length of the web from an area of relatively high temperature at the thermal interface to the development zone to a point where the strain energy is absorbed. Depending upon the film material involved, this wrinkled region can be of considerable length and, if not treated as a waste, normally extends well into the next exposure frame.

If left uncorrected, the wrinkles extending into the next exposed film region will produce pronounced density variations in the images recorded thereon. These density variations normally are well outside of thelimits which are conventionally deemed acceptable for high quality uniform imaging, which in most cases is i 0.05 density units at the mid-range of exposure (D 1.0). The apparatus of the present invention is directed towards a heated platen development system which overcomes the wrinkling problem and provides for the development of high quality images while using a minimum amount of film.

Referring now to FIG. 1, there is shown a film processing device for bringing an exposed web of dry film sequentially into a heated development zone wherein the individual images recorded upon the film are rendered visible. The development station is made up of two vertically spaced blocks or plates 12 and 13 which are preferably constructed of a material having a relatively high coefficient of thermal conductivity. In practice, the plates can be fabricated of aluminum, copper or any other suitable material exhibiting the heretofore mentioned characteristic. The upper plate 12 is provided with a generally convex shaped working surface 14 for contacting the back side, or nonemulsion side of the film. A lower plate 13 is similarly provided having a concave working surface 15 that complements the working surface contained upon the upper plate. In assembly, the plates are mounted with the two working surfaces being adjacent but in noncontiguous relation to each other so as to provide a horizontally extended cavity 17 therebetween which defines the development zone of the present system.

On the outer surface of each plate, that is, the surface opposed to the working surfaces thereon, there is placed a foil heater blanket 20 which provides input energy to the system. The blankets are both formed of a ribbon type resistant heating element 21 which is preferably sandwiched between two relatively thin sheets of plastic electrical insulating material 22. The terminal ends of each blanket are brought out, via lines 27 and 28, to two variable power supplies, an upper blanket power supply 29 and a lower blanket power supply 30, which provide energy to the heaters. Because of the high thermal conductivity of the plates, the energy delivered to the heaters is rapidly and efficiently passed through the plates to bring the working surfaces 14 and 15 thereon to a predetermined operating temperature which is at or above the thermal developing threshold temperature of the film in process.

In order to obtain a truly uniform development of high density images, it is important that the working surfaces of the two plates, which make up the developing cavity, be maintained at the same temperature. A pair of temperature sensors 32 and 33 are embedded within the plates with the sensing element thereon arranged to detect the plate temperature close to the working surfaces thereof. The sensors are both electrically connected to a comparator circuit 35, via lines 36 and 37, which is capable of determining any deviation between the temperature sensed and the desired development temperature. When the comparator circuit detects that the temperature at the working surface of either plate has fallen below or risen above the desired operating temperature, a corrective signal is generated and sent to the appropriate power supply by means of lines 40 and/or 41. In response to the corrective signal, the output of the power supply is adjusted thus bringing the system back within the desired operating condition.

In this particular embodiment of the present invention, it is contemplated that a series of exposures or frames 50 that are stored upon the web 49 are to be sequentially processed within the developing zone. However, it should be quite clear to one skilled in the art that the teachings of the present invention are not so limited to a frame by frame development sequence as herein disclosed and that more than one frame may be developed within the present apparatus without departing from the teachings of the instant invention.

The web in process consists of a series of exposed frames 50 containing input scene information recorded on the emulsion side of the film with each individual frame being separated by a relatively thin strip of unexposed film 51. The web of exposed film is carried upon a supply spool 52 and is brought emulsion side down through the developing cavity and secured to a take up spool 53. Although not shown in the drawing, an indexing drive is operatively connected to the take up spool which is adapted to advance, upon demand, the web into the developing cavity one frame at a time. The developing station 10 is located in reference to the take up spool so that each frame recorded on the web is centered within the developing cavity each time that the web is indexed. A web tensioning means such as a tensioning roll 56, is also provided in order to place a predetermined uniform amount of tension upon the web as it is being processed within the developing system.

To facilitate the positioning of exposed frames within the developing cavity, the two heating plates are adapted to move vertically between an operative or developing position to a second more extended open position. Prior to the indexing of each frame into the developing cavity, the plates are moved to the open position. Once the web has been properly indexed, the cavity is closed thereby bringing the upper working surface of plate 12 into intimate pressure contact against the nonemulsion or support side of the film. The distance be tween the two working surfaces of the plates, when in a closed position, are such that the working surface of lower plate 13 is in relatively close, but in noncontiguous relation with the exposed emulsion side of the film. During development, both a conductive transient heat transfer mechanism and a steady state adiabatic heat transfer mechanism are employed to accomplish image development. The film in contact with the upper plate is rapidly heated past the development threshold by conduction while the interior of the developing cavity is adiabatically heated by the two uniformly heated plates. The conductive heating of the film produces an efficient heat transfer at low power requirement while the adiabatic heating across the cavity provides for a more uniform development of the images.

A hydraulically actuated lifting mechanism is herein provided to facilitate movement of the plate in a vertical direction. At the outboard end of each plate is secured an end block in which a pair of hydraulic lifting cylinders 61 and 62 are secured. The opposite ends of the hydraulic cylinders are secured to a mounting plate 63 which is affixed, as for example by welding, to the processor support frame (not shown). A piston, which is located within each cylinder is arranged to hydraulically move between two extreme positions which, in turn, causes the plate to move in the direction indicated between the heretofore mentioned fully opened and fully closed position. In operation, the hydraulic control system is operatively associated with the web indexing mechanism by any suitable means so as to automatically coordinate the opening and closing of the developing cavity with the indexing of the exposed frames into and out of the development zone.

Each frame is indexed into the developing cavity and the frame then developed while tensioned against the upper platen surface. As a result, a non-uniform wrinkling of the film is produced within the boundary region adjacentto the development zone. In order to control the wrinkling problem, the platen surface of the upper plate is designed to offset or substantially eliminate the wrinkling effect thus providing for a more uniform image development which is well within acceptable density ranges for quality imaging. From test data analysis, it has been found that wrinkle control, and thus process uniformity, basically is a function of the normal pressure exerted by the platen against the film during development. Normal pressure, in turn, is directly proportional to the tension exerted upon the web and inversely proportional to the radius of curvature of the platen surface acting upon the film. Consideration of the films maximum yield stress at the developing temperature involved shows that only a finite amount of tensioning can be tolerated before material failure occurs. The principle property therefore that can be acted upon to control wrinkling is the radius of curvature of the platen surface.

The normal pressure exerted by the platen against a tensioned web is expressed by the following relationship:

where:

P is the normal pressure exerted by the platen against the film (psi), 7 is the amount of tension placed upon the film (lbs),

R is the radius of curvature of the plate (in),

W is the film width (in).

It has been further found experimentally that the amplitude of the wrinkles established within the boundary regions to the developing zone approximates a linearly decreasing function. A second relationship thus can be established to find the radius of curvature at any point along the platen surface that is required to assure uniform development of the film in the distorted web regions so as to provide for images having a uniform density within the predetermined range required. This relationship is as follows:

where:

S, is the wrinkle length on the deformed film,

S is the platen arc length under consideration wherein S at the edge of the platen where the wrinkle area first comes into contact with the platen,

P is the minimum normal pressure required to process wrinkled film so that a uniform image density within a predetermined range is produced,

P is the minimum normal pressure required to uniformly develop undistorted film to produce uniformly density of dense images with a predetermined range.

The terms for P,, and P, can be found experimentally or nnnlyticnlly for the particular film in process. Solving for the radius of curvature as a function of arc length (R,) to satisfy the pressure relationships noted above lead to the relationship:

/R( i(S)/TW I From this expression a relationship is derived for any given radius of curvature along the platen surface for processing deformed film wherein:

[ o-P2 S TW S s It will be noted that the above relationship is expressed in terms of platen curvature and arc lengths. In order to obtain a more convenient expression for any desired arc length in terms of x and y coordinates and the angle ()5, that is, the angle between a line tangent to the plate curve and the x coordinate as illustrated in FIG. 2, the following differential equation is established:

By solving the above relationships 6, 7 and 8, a platen surface can be constructed which is capable of processing wrinkled film so that the unwanted effects of the wrinkling upon image density and uniformity of development is substantially offset.

In practice, the upper platen surface, which is brought into contact with the back side of the film during processing, is provided with two discrete zones. These include a first zone M (FIG. 2) having a changing radius of curvature which is tensioned against the wrinkled deformed portion of the film, and a second zone N having a uniform radius of curvature which is tensioned against the non-deformed portion of the film during development. It should be noted that the concave working surface 15 of the lower plate is constructed so as to complement the upper plate surface and it should be understood that the surface of the lower plate is generated in a manner similar herein described in relation to the upper plate.

The upper platen surface is designed so that the radius of curvature at point S (FIG 2), wherein the amplitude of film wrinkling has attenuated to about 0, is such that the normal pressure exerted upon the film by the platen is equal to the minimum pressure required for uniform development of non-deformed film within a developing system. As noted above, this particular parameter can be found either experimentally or analytically. From point S to the entrance to the development zone at point T, the radius of curvature of the platen surface is held constant so that minimum pressure is exerted upon the non-deformed exposed frame region supported therein to produce the desired image density. From point S to point S which is located at the exit to the development zone, the radius of curvature of the platen decreases in direct proportion to the variation in amplitude of wrinkling induced in the film. The platen pressure exerted upon the film is smoothly and uniformly increased across the wrinkle area thus providing an increasing normal pressure over the film wrinkle area and insuring good thermal contact therebetween throughout the contact region. In practice, the

arc length of zone M is equal to the length of the dis-- tressed film region. By utilizing relationships 5, 6, 7 and 8 noted above, the x, y coordinates and the angle can be found for a number of points along the platen sur face whereby the desired curve can be generated-or shaped using well-known shop practices employed in the generation cam profiles or the like.

As previously noted, wrinkling of the web when processed in a conventional developing system will occur within both boundary regions. However, as graphically illustrated in FIG. 3, wrinkling produced by the present system is confined only to the entrance region to the development zone. The film located within the thermal boundary of the exit region has been previously shrunk during development and therefore tends to resist further shrinkage. This internal force, coupled with the increasing normal pressure delivered by the platen against the film within the development region, acts to resist further shrinkage in the exit boundary region. As a consequence, under the worst conditions only a minimal amount of film wrinkling is produced and is confined within a very narrow area well within the unexposed film regions connecting the two adjacent exposure frames.

While this invention has been described with reference to the structure herein disclosed, it is not necessarily confined to the details as set forth and this particular application is intended to cover any modifications or changes as may come within the scope of the following claims.

What is claimed is:

l. A heated platen surface for processing dry film having a deformed portion thereon containing a wrinkle, the amplitude of which diminishes over the length of the film and a non-deformed portion, including a first region on the platen surface for tensioning the wrinkled deformed portion upon said film, said first region having a radius of curvature that increases proportionally to the decrease in amplitude of film wrinkling whereby the normal forces acting on the deformed portion of the film decrease as the amplitude of wrinkles decreases, and

a second region on said platen surface for tensioning the non-deformed portion of said film having a uniform radius of curvature whereby a substantially uniform normal pressure is exerted upon the nondeformed portion of the film.

2. The apparatus of claim 1 having a second heated platen surface which complements the first platen described in claim 1 being positioned from said first platen at a distance that is greater than the thickness of the film in process.

8 3. The apparatus of claim 2 wherein both platens are heated to about the same temperature.

4. The apparatus of claim 3 wherein said temperature is at or above the developing threshold temperature of 5 the film.

5. ln a device for continually processing discrete exposed portions upon a web of dry film by moving said discrete portions of the web seriatim into a heated developing zone, apparatus for substantially eliminating deformations induced in the web within the boundary region at the entrance to the development zone includmg a heated platen surface within the developing portion against which each discrete portion of the web to be developed is placed under uniform tension,

said platen surface having a first region thereon arranged to contact the deformed portion of said web and having a radius of curvature that increases inversely with the amplitude of the deformation in said web whereby a higher normal force is exerted by the platen upon the deformed portion of the web containing a high amplitude of deformation and a lower normal force is exerted on the deformed portion of the web containing a low amplitude of deformation,

2 second region upon said platen surface arranged to contact the non-deformed portion of the web and having a uniform radius of curvature whereby a substantially uniform normal force is exerted over the non-deformed portion of the web during development.

6. The apparatus of claim 5 wherein the normal force acting upon the film portions containing a low amplitude of deformation are the same as the normal force acting upon the non-deformed portion of the web.

7. The apparatus of claim 6 further including a second surface positioned adjacent to said platen surface in non-contiguous relationship therewith which complements said platen surface to form a cavity of uniform depth therebetween.

8. The apparatus of claim 7 wherein both the platen surface and said second surface have means operatively associated therewith for heating said surfaces to the same temperature.

9. The apparatus of claim 5 wherein the radius of curvature on said first platen region increases substantially linearly.

10. The apparatus of claim 5 wherein the radius of curvature at any point along the first platen region is expressed by the relationship I So P is the minimum normal pressure required to develop non-deformed film within said desireddensity range,

T is the uniform tension exerted upon the web,

W is the width of the film 

1. A heated platen surface for processing dry film having a deformed portion thereon containing a wrinkle, the amplitude of which diminishes over the length of the film and a non-deformed portion, including a first region on the platen surface for tensioning the wrinkled deformed portion upon said film, said first region having a radius of curvature that increases proportionally to the decrease in amplitude of film wrinkling whereby the normal forces acting on the deformed portion of the film decrease as the amplitude of wrinkles decreases, and a second region on said platen surface for tensioning the nondeformed portion of said film having a uniform radius of curvature whereby a substantially uniform normal pressure is exerted upon the non-deformed portion of the film.
 2. The apparatus of claim 1 having a second heated platen surface which complements the first platen described in claim 1 being positioned from said first platen at a distance that is greater than the thickness of the film in process.
 3. The apparatus of claim 2 wherein both platens are heated to about the same temperature.
 4. The apparatus of claim 3 wherein said temperature is at or above the developing threshold temperature of the film.
 5. In a device for continually processing discrete exposed portions upon a web of dry film by moving said discrete portions of the web seriatim into a heated developing zone, apparatus for substantially eliminating deformations induced in the web within the boundary region at the entrance to the development zone including a heated platen surface within the developing portion against which each discrete portion of the web to be developed is placed under uniform tensioN, said platen surface having a first region thereon arranged to contact the deformed portion of said web and having a radius of curvature that increases inversely with the amplitude of the deformation in said web whereby a higher normal force is exerted by the platen upon the deformed portion of the web containing a high amplitude of deformation and a lower normal force is exerted on the deformed portion of the web containing a low amplitude of deformation, a second region upon said platen surface arranged to contact the non-deformed portion of the web and having a uniform radius of curvature whereby a substantially uniform normal force is exerted over the non-deformed portion of the web during development.
 6. The apparatus of claim 5 wherein the normal force acting upon the film portions containing a low amplitude of deformation are the same as the normal force acting upon the non-deformed portion of the web.
 7. The apparatus of claim 6 further including a second surface positioned adjacent to said platen surface in non-contiguous relationship therewith which complements said platen surface to form a cavity of uniform depth therebetween.
 8. The apparatus of claim 7 wherein both the platen surface and said second surface have means operatively associated therewith for heating said surfaces to the same temperature.
 9. The apparatus of claim 5 wherein the radius of curvature on said first platen region increases substantially linearly.
 10. The apparatus of claim 5 wherein the radius of curvature at any point along the first platen region is expressed by the relationship 